Sputtering refers to a process which involves the coating of a semiconductor wafer or other substrate mounted within a processing chamber, which wafer is biased electrically with respect to a spatially opposed target made with the material to be sputtered. An inert gas is introduced into the chamber at low temperature and an electric field is applied to ionize the gas. Ions from the gas bombard the target and dislodge atoms from the target which are subsequently deposited onto the wafer or other substrate.
Prior methods of fabricating aluminum alloy sputtering targets included the steps of billet homogenization, target formation and final recrystalization. The billet homogenization was typically done at temperatures lower than the solidus temperature in order to inhibit grain growth.
One method of controlling cyrstallographic orientation is disclosed by Pouliquen, U.S. Pat. No. 5,087,297, herein incorporated by reference. Pouliquen discloses slow forging a heated billet to produce a preferred &lt;110&gt; grain orientation. The method of Pouliquen heats a 4 inch by 7 inch billet having a grain size of 1 mm to a temperature of 572.degree. F. The heated billet is then slowly forged from a thickness of 7 inches to a thickness of 11/2 inches. The billet is then machined to final dimensions to result in a sputtering target having a 1 mm grain size oriented in the &lt;110&gt;direction, as determined by x-ray diffraction. The method of Pouliquen deforms the billet at a rate of 0.5 inches-4 inches/minute at a temperature of 550.degree. F. to 900.degree. F.
Another manufacturing method is disclosed by Fukuyo, U.S. Pat. No. 5,456,815, herein incorporated by reference. Fukuyo provides for hot working of an Al-3.0 wt. % Cu at 520.degree. C., followed by warm-working at 275.degree. C. in a working ratio of between 1.8 and 2.0, followed by heat treating at a temperature between 420.degree. C. and 470.degree. C. for 1 hour.
The solution treatment raises the temperature of the billet higher than the solidus temperature of the alloy to disburse the second phase precipitates, such as Cu, into the Al matrix. Previously, such solution treatment resulted in significant grain growth caused by the loss of the pinning effect of the precipitates on grain front boundary movement. In order to refine the grains of the solution treated billet, the billets are deformed at room temperature or at temperatures up to 500.degree. C. Typically, the deformation of low alloy aluminum materials results in a cubic structure resulting in a grain orientation with a high percentage of (220) or (200) grain orientation.
The prior processes provide either (200) or (220) oriented structure and/or large second phase precipitates of up to 10 microns. Targets having a strong (200) or (220) orientation generate films having poor uniformity. Poor conductivity of the large second phase precipitates generate localized arcing during sputtering, resulting in a high particle density or in large particles deposited on the wafers.
In order to improve the efficiency of integrated circuit manufacture, lower cost of manufacturing and improve productivity and yield, it is desired to improve the deposited film uniformity and increase the deposition rate. It is known that film uniformity and sputter deposition rate are related to the crystallographic orientation of the sputtering target which affects the distribution of material ejected from the target. It is also known that the sputtering of atoms from the target occurs preferentially along the close packed directions the target material and that a near random grain orientation provides better uniformity of the sputtered films.